Monday, July 05, 2010

Rasmus Benestad: negative feedbacks are almost impossible

Rasmus Benestad of Real Climate wrote a long text,
A simple recipe for GHE,
that mixes several goals. (GHE stands for "greenhouse effect.") It says that "nothing is changing" about the catastrophic man-made climate change; it is an elementary yet semi-technical introduction to the Earth's energy budget and the greenhouse effect; and it offers some cheap attacks against all ideas in the climate science that are not helpful to enhance the people's belief in the catastrophic man-made climate change.

At the beginning, we learn that most of the recent polls must be wrong and that the people may be increasingly afraid of global warming. Well, let me mention a single number: "global warming" hits at Google News - in the last 30 days - have dropped from the peak well above 50,000 a few years ago to 10,000 or so (and they were below 10,000 for a while).

Benestad says that
In any case, the science behind climate change has not changed.
That's too bad because if the science behind climate change hasn't changed for several years, it means that those who make research of climate change shouldn't have been paid for several years - and they should either return the salaries that were not backed by the actual research work, or they should be punished in an alternative way. The very purpose of scientific research surely is to change the science behind the discipline we study.

In the second part of the text, he says lots of basic things about the energy propagation in the atmosphere, light absorption, greenhouse effect, dependence of temperature on the altitude, and so on. I would agree with a big portion of this segment of Benestad's text.

Don't get me wrong, there are many breathtakingly unpedagogical errors that make Benestad's text unusable as an introduction to these problems. For example, his Figure 1 shows the black body radiation flux density at two temperatures, that of the Sun and that of the Earth, and the "Sun's" infrared emission is bigger than the Earth's infrared emission! (And they would asymptotically coincide for very low frequencies of electromagnetic radiation.)

This is of course correct for two black bodies located at the same place.

But if this were the case for the radiation going through our atmosphere, the greenhouse effect would cool the surface. Of course, the bizarre "infrared dominance of the Sun" only occurs because Benestad didn't reduce the Sun's infrared flux - and all the flux, for that matter - by the (big and squared) distance of the Sun from the Earth! His "Sun" has nothing to do with the fluxes we observe on the Earth. There are probably many crazy confusions of this type in his text but let me only mention one more:
This is because energy cannot just be created or destroyed (unless it involves nuclear reactions or takes place on quantum physics scales).
Mr Benestad apparently believes that both nuclear reactions and quantum mechanics violate the energy conservation law! Well, they don't, Mr Benestad. As Emmy Noether has shown, the energy is conserved whenever the laws of physics are invariant under translations in time.

However, I still praise Benestad for trying to be a bit technical; in the comment section, he is mostly criticized for doing so by the "activists" and he surely notices that it is the skeptics who have a deeper understanding for the science (and even for his text).

For example, John Atkeison, a self-described activist, recommends to replace Benestad's text by a simpler text, one that claims that "global warming walks and quacks like a duck, so it must be a damn duck", which is "the kind of post [he] need[s] to keep [his] level of understanding at a decent level, so [he] can play [his] role." The dumber you are, the better AGW activist you become. 95% of the AGW hysteria depends on the 5% of the top idiots.

The Real Climate author also tries to humiliate the effect of solar variations etc. on the climate, promoting his purpose-driven paper with Gavin Schmidt, another "Real Climate" member, along the way. However, the real key question is concerned with the magnitude of the CO2-induced warming - and that means that the real question is about the feedbacks.

Negative feedbacks are an inconvenient truth

In the first paragraph about the feedbacks, Benestad mentions a few players in the atmosphere - vapor, clouds, snow, ice, vegetation - and tries to create the impression that all feedbacks in the climate system are positive.

Of course, the positive feedbacks are helpful for the catastrophic man-made climate change, so even the most vague ideas about their functioning are immediately accepted by Benestad as irreversible facts. On the other hand, negative feedbacks are not helpful, so they're criticized under the headline "Controversy?".

That's what the Real Climate-style "scientists" call an impartial perspective.

Needless to say, a criticism of negative feedbacks as a matter of principle is utterly preposterous. The Universe is dominated by negative feedbacks. All stable and metastable systems have negative feedbacks responding to pretty much any kind of a perturbation. I am just reading a nice big textbook of ecology that a TRF reader kindly sent me and one can say that most of the book is about negative feedbacks - and they have many forms. That's surely how life (and not only life) responds to pretty much any external perturbation.

When we emit X tons of CO2, we could also claim that those X tons of CO2 will induce some additional greenhouse effect. But the first thing to notice is that a part - about 50% - of X is actually abruptly absorbed by the ocean and the biosphere. This is the first negative feedback in the CO2-temperature-related network of effects. All the actual impacts of the atmospheric CO2 will be reduced because of that.

It shouldn't be hard to understand that such feedbacks are omnipresent. When something becomes more abundant - e.g. CO2 or heat - objects and processes that "consume" this CO2 or heat (or anything else) become more frequent because of their easier access to the "nutrient", which is why they act against the initial perturbation.

It's the content of the Le Chatelier principle. It applies to all stable systems. You may know it from your chemistry classes at the basic school. Paul Samuelson has imported the principle to economics. In fact, he realized that the number of these negative feedbacks increases if you study the system at longer time scales - because new, slower negative feedbacks that may consume the extra "nutrient" emerge if you wait for some time. It may be true that there are short-term positive feedbacks but the net feedbacks measured in the long run are likely to be negative.

Benestad is either ignorant about these basic principles or he hides them. Instead, he offers the following bizarre criticism of the very concept of negative feedbacks:
There have been claims of negative feedbacks, such as the “iris effect“. One would expect negative feedbacks in general to dampen the response to most forcings, unless they involve a particular process that is active for a particular forcing. In other word[s], why would a negative feedback act for GHGs but not for solar forcing? Many feedbacks, such as changes in atmospheric moisture, cloudiness, and atmospheric circulation should be similar for most forcings.
Well, negative feedbacks may respond in a similar way to many forcings, indeed. They probably do. Why does Benestad try to pretend that they don't - or that the skeptics claim or need to claim that they don't? It's also true that some feedbacks could depend on the particular perturbation: some of them may operate only in the stratosphere, or only in the lower or upper troposphere, and reduce or amplify effects in those parts of the atmosphere only.

But yes, it's almost certainly true that both greenhouse and solar perturbations are subjects to similar feedbacks and many of them are negative.

In particular, the variations in the solar output are probably damped by negative feedbacks, too. That is, among other things, the simplest interpretation of the very basic fact behind the Faint young Sun paradox, namely the observation that the Sun was 30% weaker a source of energy at the beginning of the Earth's life but it still seems that the Earth's temperature was close to the present one (instead of being much cooler).

Well, there had to be something that kept the temperature close to the present temperature. It's not unreasonable to believe that this mechanism was actually not accidental: there may exist mechanisms that really try to keep the Earth's temperature within a window even if the forcings are substantial.

Benestad's criticism continues as follows:
Another question is why we do see a global warming trend if the negative feedbacks were most important (Figure 5).
Well, we don't see any "global warming trend". We see de facto random fluctuations - similar to the natural temperature variations of a human body, as Richard Lindzen likes to say. To show how huge the hypothetical "global warming trend" is, Rasmus Benestad expands the temperature graph from the last 150 years in the y-direction. He could have made the story even more impressive:

The global warming was really fast, wasn't it? One-half of the readers may be impressed by similarly cheap sleights-of-hand and Benestad et al. clearly realize this fact and build upon this fact. These are small points but they help to show the incredibly biased attitude of the likes of Benestad. In his discussion of the black body etc., he actually talked about the absolute temperature - i.e. temperature in Kelvin degrees. The correct graph of the "global warming trend" in the last 150 years actually looks like this graph of the absolute temperature:

Even if you shift/click the picture and zoom it in, the "global warming" variations will only be moving the graph by 2 or 3 pixels up or down simply because the temperature kept on changing between 287 and 288 Kelvins or so and the picture only has 564 pixels of height. (Sorry, I probably drew 277-278 but it makes no qualitative difference.)

It's a very inconvenient truth but my chart with the flat line is a much more honest representation of the temperature that is relevant for the calculations of the Earth's energy balance. Even if you chose the conventional degrees of Europe - the Celsius degrees - the graph of the monthly global mean temperatures since 1850 would look like this:

This is the global warming in Celsius degrees - and you know that the readings in Celsius degrees can change by a lot, relatively speaking. (The Fahrenheit graph would look even flatter than the Celsius graph because 0 °F is between 0 °C and 0 K.) The global warming in the last 150 years is just not worth talking about and Benestad's y-inflated picture is simply dishonest.

But let me return to the more complex topic, the feedbacks.

Benestad mentions that positive feedbacks tend to produce instabilities but he doesn't dare to reveal the obvious fact that it's a problem - a source of tension with the apparently stable history of our planet. See Why feedbacks can't be both high and positive. Indeed, small variations are often sufficient to extend stable positive feedbacks to the unstable ones which makes even the stable positive feedbacks dangerous - and potentially inconsistent with the longevity of the Earth.

He asks a few simple questions and he pretends that these questions don't have any answers - or that it's a heresy to answer any of these questions. It seems that the readers are only allowed to treat the questions as rhetorical ones. For example,
The point about negative feedback also brings up another interesting issue: Negative feedbacks usually act to restore a system to a particular zero-level state. What would the zero-state be for our climate? No greenhouse effect or some preferred level of greenhouse warming?
Well, as long as we are allowed to make observations of the reality, it's easy to answer them. Just look at the history of the Earth's climate. The global mean temperature has arguably been between 5 °C and 25 °C (i.e. 278 and 298 Kelvin) during the vast majority of the Earth's history. That's the interval that all the negative feedbacks were trying to restore. We may misunderstand the precise way how they managed to do it - but it's our problem: it's a challenge for science. However, the observational data speak in a pretty clear language.

You may complain that the interval is "preferred" and democracy requires no one to be preferred. ;-) But Nature will keep on ignoring your complaints. Nature uses Her own rules to determine what the temperature on Earth should be, how it may change or should change, and how it shouldn't change or can't change. The purpose of science is to understand these rules of Nature rather than trying to impose ideologues' own rules upon Nature.

So it's just a fact that the global mean temperature was kept in such a window and it's pretty likely that this regulation had to be achieved by some negative feedbacks because negative feedbacks protect us against "unlimited random walks" or even "exponentially growing perturbations".

Do you have a problem with the assertion that the global mean temperature that the feedbacks are trying to restore are defined by an interval rather than a well-defined single number? Well, that's just the way the Earth operates. If Mr Benestad dislikes this basic fact about Nature, he may ask another Universe for the political asylum.

The global mean temperature simply does oscillate much like anything else that can a priori oscillate. The human body starts to sweat when it's really warm - above 39 °C. That's its method to regulate the temperature. We shiver when it's cold outside, too. However, despite these regulating "feedbacks", it's still true that our body temperature is routinely and pretty randomly moving between 36 and 37.5 °C and there's absolutely nothing unnatural about these oscillations. That's how the bodies function - and the climate system is no different. A Celsius degree of variations is simply not something we should be shocked by.

There are many positive feedbacks in the atmosphere (and oceans) but many of them only operate in the short run and they are eventually beaten by stronger negative feedbacks in the long run. For example, the tropical depressions often like to grow into hurricanes. That's clearly a positive feedback - there are good reasons why the speed of the winds often increases when the conditions are appropriate. However, the hurricanes never grow infinitely large. At some point, after a few weeks, other processes will terminate the hurricanes; these processes may be viewed as negative feedbacks.

Benestad continues in his claim that the Earth should have no special temperature - this is kind of cute because very similar sentences have been said by the skeptics (however, they correctly spoke about the preferred temperature that we should achieve forever - which doesn't make much sense - while Benestad tries to claim that the Earth actually had no preferred temperature - and it obviously had such a temperature at every moment):
There is already a natural GHE that, together with other atmospheric effects, can account for about 32 °C higher global mean surface temperature. What makes this state so special, and can we explain the present natural GHE in the presence of negative feedbacks (consider starting from a state with no GHE)?
What makes it special? Well, it must clearly be a solution to some properly calculated constraints that take the rough environmental variables on the Earth into account. It's an effective law of Nature, some equations, or the solution to an optimization problem, if you wish. Whether or not we fully understand these constraints, and we surely don't understand them entirely, they're facts of Nature. Science has to understand them. A scientist can't get rid of this task by denying the natural climate change or the existence of negative feedbacks that obviously play a critical role in the regulation of the temperatures.

The final paragraph written by Benestad is cute, too:
Hence, claims of negative feedback [are] controversial because all these tough questions then need to be addressed. We can write down a simple recipe for the GHE, but it is indeed challenging to reconcile a presence of a negative feedback with our observations, or explain the current observed global warming in any other terms.
Claims of negative feedbacks - and they are a necessary concept in all sensible science because they are something that is absolutely omnipresent in nearly all systems in Nature - are supposed to become controversial just because an insane quasi-religious bigot writes an incoherent and illogical rant against the very concept of negative feedbacks and because he uses the term "tough questions" for his elementary questions he should have asked to his undergraduate instructors before he should have been dismissed from the college.

Well, let me make it clear that there's nothing controversial about negative feedbacks. In this battle between negative feedbacks and Rasmus Benestad, it is the latter who is an utterly controversial crackpot. The existence of crackpots may make basic concepts of science controversial among crackpots - and the remaining readers of Real Climate, if there are any - but it can't make it controversial in the real science.

And that's the memo.


  1. Well done.
    The essay you deconstruct so well sounds like a climate version of the Captain's testimony in the Caine Mutiny.

  2. It looks like a duck, it quacks like a duck, so it must be a duck-monster that's going to bite your dick off and rape your children.

  3. The solar effect is based on the existence of the negative feedback. The argument is that increased solar activity reduces the iris effect.

  4. Lubos

    The debate over AGW has given me a broader interest in climate science, not just AGW. Are there any resources for newbies you would recommend?